Who is Mother from A Summons to Memphis and what is their importance?

Phillip, Georgie, Betsy, and Josephine's mother is described as kind and caring. She sometimes seemed happy with the family's move to Memphis and her newfound freedom, but at other times she mocked it. After her health began to fail, Mother never regained her strength. She is dead at the beginning of the story, but is briefly mentioned in flashbacks by Phillip in other parts of the story.